1. Field of the Invention
The present invention relates to an electric motor having a speed reducing mechanism.
2. Description of Related Art
One previously proposed motor used in, for example, a vehicle wiper system includes a housing (gear housing) and a housing cover. The housing supports a speed reducing mechanism and an output shaft, and the housing cover is connected to the housing. The motor also includes electric circuit components, such as a movable contact, stationary contacts, terminals and noise limiter elements. Here, the movable contact is rotated synchronously with rotation of the output shaft, and the stationary contacts are slidably engageable with the movable contact. In one such a motor disclosed, for example, in Japanese Unexamined Patent Publication No. 7-245904 (corresponding to U.S. Pat. No. 5,656,878), a receiving portion, i.e., a storage case, is formed in an outer surface of the housing cover (outer surface that is opposite from the housing), and the terminals and the noise limiter elements are received in the receiving portion, so that electrical insulation of the terminals and the noise limiter elements with respect to the movable contact and the stationary contacts arranged in an inner surface of the housing cover is ensured.
However, in this motor, a cover, which closes the receiving portion, is required. Furthermore, it is required to water tightly seal the cover by, for example, application of sealant.
There has been proposed another motor, which includes a unit (unit plate) having the electric circuit components described above. The unit plate is received inside the housing and the housing cover. However, in such a motor, when a size of the motor is reduced, a space between the unit plate and the movable contact is reduced. Thus, it is difficult to achieve the electrical insulation between the terminals and the movable contact (moving member).
Furthermore, an example of the motor having the unit plate, which is attached to an inner surface of the housing cover, is disclosed in Japanese Unexamined Patent Publication No. 8-275441 (corresponding to U.S. Pat. No. 5,691,585). This motor includes a case frame (i.e., a housing), which receives a speed reducing mechanism, a case cover (i.e., a housing cover), which closes an opening of the case frame, and a support plate (i.e., a unit plate), which is attached to an inner surface of the case cover. The case cover includes a connector housing part. The connector housing part is shaped into a tubular form, which extends in a direction perpendicular to the closing direction, and is engaged with an external connector. The support plate includes a terminal side half and an output shaft side half, which are separately provided. The support plate is formed as a unit, in which electric circuit components that include power supply connector terminals are secured. When the support plate is installed to the case cover, the power supply connector terminals are received in the connector housing part. When the external connector is fitted to or engaged with the connector housing part, the power supply connector terminals are connected with corresponding terminals of the external connector. In the above-described motor, a shaft support arrangement and securing projections, which support a contact plate (i.e., a movable contact) having a predetermined pattern, protrude from a surface of the case cover, to which the support plate is installed. The support plate (more specifically, the output shaft side half) includes a through hole for receiving the shaft support arrangement and through holes for receiving the securing projections.
In the above motor, at the time of assembly, first, the support plate is angled relative to the case cover and is positioned to guide and to insert the power supply connector terminals into the connector housing part. Then, the support plate is gradually tilted downwardly such that the support plate is arranged along the inner surface of the case cover, and the shaft support arrangement and the securing projections are received in the corresponding through holes of the support plate. That is, the support plate is angled and is lowered (i.e., approached) toward the case cover in such a manner that the support plate is slid to guide and to insert the power supply connector terminals into the connector housing part. Then, the angled support plate is further lowered (i.e., approached) toward the case cover while positioning the support plate in such a manner that the shaft support arrangement and the securing projections are received in the corresponding through holes of the support plate. Thus, the two or more directional movements need to be simultaneously performed to install the support plate to the case cover. As a result, in the above motor, the installation operation is disadvantageously complicated and becomes tedious. Furthermore, when automatic assembly is performed, this will cause an increased complexity of an assembly device (device should be capable of performing the tilt positional control and is also capable of simultaneously performing the two or more directional movements), resulting in an increase in the manufacturing costs.
Furthermore, in the above motor, stationary contact members, which are stationary relative to the motor, are provided in a slidably engageable manner with respect to the movable contact. With this arrangement, rotation (angle) of the output shaft can be measured. Through engagement/disengagement between the stationary contact members and the movable contact according to the pattern, a wiper arm (wiper blade) is moved to a predetermined stop position located along a lower edge of a vehicle window glass and is automatically stopped even when the wiper arm (wiper blade) is still in a wiping position.
However, in the above motor, the movable contact is supported by the housing cover, and the stationary contact members, which are slidably engageable with the movable contact, are secured to the support plate, which is, in turn, secured to the housing cover. Thus, a positional relationship between the movable contact and the stationary contact members is affected by assembly errors of the support plate and of the housing cover. When the positional relationship between the movable contact and the stationary contact members is deviated from a predetermined positional relationship, measurement accuracy of a rotational angle of the output shaft, which is measured through the movable contact and the stationary contact members, is disadvantageously reduced. Particularly, in the case of the wiper motor, this will cause substantial deviation of the stop position of the wiper arm (wiper blade), which is connected to the motor through a link mechanism, from a predetermined stop position. Alternatively, this will cause substantial deviation of a reverse position of the wiper arm.
Thus, it is an objective of the present invention to provide a motor, which includes a movable contact and a unit plate securely holding electric circuit components and which allows a reduction in its size and effective electrical insulation.
It is another objective of the present invention to provide a motor, which includes a housing cover provided with a connector housing part shaped into a tubular form extending in a direction perpendicular to a closing direction of the housing cover and which allows easy installation of a unit plate, to which power supply terminals to be received in the connector housing part are secured, into the housing cover.
It is a further objective of the present invention to provide a motor capable of improving measurement accuracy of a rotational angle of an output shaft, which is measured through a movable contact and a stationary contact member.
To achieve the objectives of the present invention, there is provided an electric motor that includes a motor main body, a housing connected to the motor main body, a speed reducing mechanism received in the housing, a housing cover connected to the housing, and a unit plate secured to the housing cover in opposed relationship to the housing. The motor main body includes a rotor and a plurality of brushes, through which electric current is supplied to the rotor. The housing includes an opening. The speed reducing mechanism reduces rotational speed of the rotor and includes an output shaft to output rotational force. The housing cover closes the opening of the housing and includes a connector housing part, to which an external connector is fitted in a fitting direction, and the connector housing part is shaped into a tubular form that extends in the fitting direction of the external connector. The unit plate holds a plurality of electric circuit components. The plurality of electric circuit components includes at least one power supply terminal that includes first and second ends. The first end of each power supply terminal is connected to a corresponding one of the plurality of brushes, and the second end of each power supply terminal is connected to a corresponding terminal of the external connector. The housing cover further includes at least one guide wall, which extends in a direction generally parallel to the fitting direction of the external connector to guide the unit plate in such a manner that the second end of each power supply terminal held by the unit plate is received in the connector housing part at time of installing the unit plate to the housing cover.
To achieve the objectives of the present invention, there is also provided an electric motor that includes a motor main body, a housing connected to the motor main body, a speed reducing mechanism received in the housing, a housing cover connected to the housing and a unit plate secured to the housing cover in opposed relationship to the housing. The motor main body includes a rotor and a plurality of brushes, through which electric current is supplied to the rotor. The housing includes an opening. The speed reducing mechanism reduces rotational speed of the rotor and includes an output shaft to output rotational force. The housing cover closes the opening of the housing. The unit plate holds a plurality of electric circuit components. The electric motor further includes a rotator, which is rotated synchronously with rotation of the output shaft of the speed reducing mechanism and includes a movable contact, which is rotated together with the rotator and is made of a conductive plate that is configured to have a predetermined pattern. The unit plate includes a rotation support arrangement, which rotatably supports the rotator. The plurality of electric circuit components includes at least one stationary contact member. Each stationary contact member includes a contact section, which is slidably engageable with the movable contact.